This invention relates to injecting foam into a pipeline and to a novel plug which forms an important part of the apparatus for doing this.
In order to make clearer what is being done, it may be said that the present invention is used for injecting chemicals that kill root growth in sewers; these chemicals are preferably delivered in the form of foam which clings to the wall of the sewers and to obstructions such as tree roots and grease inside the sewers. The specially prepared foam (described in other U.S. patents) acts to reduce such growth as tree roots and to kill the roots lying within the sewers.
The closest art known to the applicants is that disclosed in their earlier U.S. Pat. No. 3,874,926. In that patent, foam is injected into a pipeline by means of a tube having secured at its end an inflatable plug. While this structure has proved satisfactory in many instances, such as for treating house sewers and building sewers, it also has run into difficulties in other conditions. Thus, when one wanted to treat a long pipeline, such as a sewer in between two manholes, and started injecting foam according to the method and apparatus described in U.S. Pat. No. 3,874,926, back pressure would build up, and the length of sewer pipe or other pipeline that could be treated would be rather short because the building up of this back pressure causes foam to flow back up building service lines and to enter house fixtures. In other words, when the injected foam went out the end of the tube, it would be pushed along the pipe by the pressure of the succeeding foam, but soon the expelled foam would build up a resistance against the newer oncoming foam, and the resistance or back pressure would rise. Soon, the resistance would be such that the pressure of the newly issuing foam would be forced into sewer taps and service lines and to flow back up house sewers into the house fixtures, or into such fixtures in other buildings.
The major purpose of the present invention is to address this problem and to provide a system wherein a longer length of pipeline can be processed in each treatment without requiring large additional pressures.
Another problem of the former invention was that it was substantially limited in use to service lines, such as building sewers. Yet problems very similar to those found in building sewers occur also in the main sewers. The present invention enables practical treatment of main sewers as well as in service lines connecting homes and other individual users to the main sewers. The present invention is also superior in enabling treatment of the lower portions of such branch lines from the main sewers; by controlling the foam pressure in the main sewer, some foam can enter the service sewers and still be kept from entering into the dwellings themselves.
It has also been found that sewer mains often have such heavy root growths that they obstruct movement of the foam and cause the line foam pressure to be excessive. With this invention it becomes possible to extend the foam discharge tube beyond the root obstruction; then, after the pipe above the root growth has been filled with foam, the entire length of the section of pipe to be treated can be filled with foam without using pressures sufficient to force the foam up the building service lines far enough to extrude into the fixtures.
Thus, among the objects of the present invention are: to provide a novel type of inflatable plug and a system related to it in which a longer length of sewer pipe can be treated while other factors remaining substantially the same; to provide a system which can safely be used to treat main sewers; to provide a system having greater flexibility and adaptability than that formerly obtainable; and to provide a plug and system which is better suited to use in service line connections of the individual users to sewers than is otherwise obtainable by the present art.